This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Determining when to flower is one of the most important decisions a plant must make in its lifetime, and understanding the ways plants do this remains one of the most important challenges to plant biologists today. It is known that many plants flower in response to photoperiod (the relative length of day and night) and, for over eighty years, researchers have focused their attentions on elucidating the molecular events that initiate flowering in photoperiodic plants. In the literature, the role of the plant hormone ethylene in this process remains controversial. The research proposed here aims to explore the role of ethylene in the photoperiodic flowering response of the model short-day photoperiodic plant Pharbitis nil Chois cv Violet (Japanese morning glory). Objectives of this research are (1) to determine if ethylene production in P. nil is regulated by photoperiod, (2) to investigate the site of ethylene biosynthetic control in response to photoperiod, and (3) to determine if ethylene alone can induce flowering in P. nil seedlings in lieu of photoperiod. Results of this work will further our understanding of photoperiodic flowering in plants and may shed light on various human health disorders linked to defects in the circadian clock.